The present invention relates to a method and apparatus of automatically switching the operation mode between cooling and heating in an air conditioner with cooling and heating functions.
A conventional technique for automatic change-over between the cooling mode and the heating mode of an air conditioner was disclosed in Japanese Laid-Open Utility Model No. 59-72437 in 1984. The control of the heating/cooling operation mode switching as performed by this air conditioner involves detection of an outdoor temperature and performing a cooling operation when the measured outdoor temperature is higher than a preset temperature and a heating operation when it is lower than the setting. The mode switchover is performed periodically according to an outdoor temperature which is detected repetitively at specified intervals after the start of operation. An operation mode is determined at specified intervals so that variations in outdoor temperatures among morning, day and night times can be reflected in the automatic control of air conditioning.
In such conventional techniques as mentioned above, the cooling and heating modes are changed over according to a change in outdoor temperatures. This type of control, however, requires provision of an outdoor temperature detector. The location of the temperature detector is critical and variations in the conditions in which the temperature detector is mounted can be the cause of erroneous operation of the air conditioner. That is, the control is affected by whether the temperature detector is located in a place subjected to direct sun rays, or in the shade, or where air stagnates, making an appropriate switchover between the cooling mode and the heating mode difficult.
Since the cooling and heating operation is controlled according to the outdoor temperature, the conditions in which the occupants of the air-conditioned room require cooling or heating may not coincide with the conditions derived from the outdoor temperatures. The result is that an appropriate changeover of cooling and heating cannot be performed.
In the light of these problems, an attempt was made to control the selection of the cooling or the heating mode by the difference between an air-conditioned room temperature and a desire temperature setting, as disclosed in Japanese Laid-Open Utility Model No. 59-67738 in 1984. This attempt has a drawback in that a temporary change in the load in the air-conditioned room, which might be encountered every time that a door is opened or closed or when the number of occupants of the room changes, may result in unnecessary switchover of the operation mode of the air conditioner according to the temperature variation in the room.
It is possible to combine the above two conventional techniques to develop a method that detects a room temperature at predetermined intervals and changes or sets the operation mode. This method, too, has a problem in that when the moment of a temporary load change coincides with the moment of the periodical temperature measurement, a similar erroneous operation may result.